Capabilities of overriding CSS in HCM Redwood pages

Summary:

Is there a way to override the CSS of the HCM application without affecting future upgrades? Specifically, we are looking to customize the look and feel of elements such as buttons, headings, font size, and font family, to adjust the theme of the existing Redwood pages.
below are the 2 sample requirements' from our client… pls let us know if its feasible
We have a create button in this page and we need to change the color, size of the button and the border radius. When we try inspecting the element, we couldn’t find any id attached to the same.